masah

Q:

1. If a person fulfils all the four faraiz of wudhu and puts on the khuffayn, can he offer salah?

2. Later after performing full ablution, can he wipe over that (do masah on khuffs and read salah)?

3. The farz of washing the feet,including heels. Does a person have to pass water i .e. do khilaal between fingers? Is it a farz too?

Q: If we perform Salaah behind an Imam who did not make masah of the neck and did not wash his feet. He only made masah on his ordinary cotton socks.  Will the Salaah of the Imaam be valid and will the Salaah of the muqtadis be valid?